polymyxin

A mixture of antibiotic substances obtained from cultures of Bacillus polymyxa (B. serosporus), an organism found in water and soils and obtainable as a crystalline hydrochloride; all are polypeptides containing various amino acid s and a branched-chain fatty acid, usually (+)-6-methyloctanoic acid. There are several polymyxins, ( e.g., designated A, B₁, C, D, E, M, T), which are about equally effective against Gram-negative bacteria, but which differ in toxicity, p. E (colistin) and p. B being the least toxic. SEE ALSO: colistin sulfate, colistimethate sodium.

- p. B sulfate an antibacterial effective in tularemia, brucellosis, Pseudomonas infections, and urinary tract infections, but used systemically only for severe infections not responsive to less toxic agents; it is also used locally. P. B is a mixture of p. B₁ and p. B₂.

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poly·myx·in .päl-i-'mik-sən n any of several toxic antibiotics obtained from a soil bacterium of the genus Bacillus (B. polymyxa) and active against gram-negative bacteria

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poly·myx·in (pol″e-mikґsin) the generic name for five polypeptide antibiotics (designated A, B, C, D, and E) derived from strains of the soil bacterium Bacillus polymyxa, having specific activity against gram-negative bacteria, including Pseudomonas aeruginosa, Proteus vulgaris, Escherichia coli, Haemophilus influenzae, and Klebsiella pneumoniae. The least toxic members of the group are polymyxins B, usually used in the form of the sulfate salt, and E (see colistin).